Vulcanizable acrylic elastomer composition

ABSTRACT

A vulcanizable acrylic elastomer composition, which comprises copolymers of at least one of (a) an alkyl acrylate having an alkyl group having 1 to 8 carbon atoms and (b) an alkoxyalkyl acrylate having an alkoxyalkyl group having 2 to 8 carbon atoms, (c) an epoxy group-containing vinyl monomer and (d) α,β-unsaturated carboxylic acid aryl ester, and (1) a disphenyl phthalate and (2) a quaternary ammonium salt or a phosphonium salt, and (3) at least one of a urea and a guanidine as cross-linking agents.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a vulcanizable acrylic elastomer composition, and more particularly to a vulcanizable epoxy group-containing acrylic elastomer composition.

2. Description of the Prior Art

Vulcanizable systems of acrylic elastomers having epoxy groups as cross-linking sites generally contain polyamines, polyamine salts, dithiocarbamates, organic carboxylic acid ammonium salts, imidazoles, etc. as cross-linking agents. However, these vulcanizable systems require a prolonged secondary vulcanization time, because of lower vulcanization rates, as compared with vulcanizable systems of acrylic elastomers containing halogens or active halogens as cross-linking sites, for example, vulcanizable systems containing sulfur or sulfur donor compound-alkali metal salt of fatty acid, trithiocyanuric acid-alkali metal salt of fatty acid, dithiocarbamates, etc. as cross-linking agents, and furthermore they have such disadvantages that the secondary vulcanization products have poor compression set and heat resistance.

However, the acrylic elastomers having epoxy groups as cross-linking sites have such an advantage as a lower metallic corrosion and thus improvements of the vulcanization rate and the compression set have been investigated for the effective utilization of acrylic elastomers having epoxy groups as cross-linking sites.

That is, the following cross-linking agents have been proposed for the vulcanizable system:

Japanese Patent Application Kokai (Laid-open) No. 61-26620 proposes compounds containing at least two carboxyl groups in the molecule-quaternary ammonium salt or phosphonium salt;

Japanese Patent Application Kokai (Laid-open) No. 61-235424 proposes polycarboxylic acid anhydrides-quaternary ammonium salt or phosphonium salt;

Japanese Patent Application Kokai (Laid-open) No. 62-236849 proposes polycarboxylic acids (anhydrides)-quaternary ammonium salt or phosphonium salt-urea;

Japanese Patent Applications Kokai (Laid-open) Nos. 63-57628 and 63-57629 propose organic compounds having at least two --CXNHCY-- bonds (wherein X and Y: O or S) in the molecule-quaternary ammonium salt or phosphonium salt (-compound having a urea bond or thiourea bond); and

Japanese Patent Application No. 63-218752 proposes organic compounds having at least two --CXNHCY-- bonds (wherein X and Y: O or S) in the molecule-guanidine-based compounds.

As to acrylic elastomers having epoxy groups as the cross-linking sites in combination with other cross-linking sites or their vulcanizable systems, the following acrylic elastomers have been proposed:

Japanese Patent Application Kokai (Laid-open) No. 61-26621 proposes acrylic elastomers having epoxy groups and carboxyl groups in combination with the vulcanizable system based on quaternary ammonium salt or phosphonium salt-urea or amide; and

Japanese Patent Application Kokai (Laid-open) No. 61-73708 proposes acrylic elastomers comprising copolymers of acrylic acid ester-dienic monomer-epoxy group-containing vinyl monomer (-monovinylic or monovinylidenic monomer).

However, these acrylic elastomers or their vulcanizable systems also require a secondary vulcanization in order to obtain vulcanization products having a high compression set. Furthermore, changes in the physical properties in the normal state before and after the secondary vulcanization are large and no higher heat resistance is obtained.

SUMMARY OF THE INVENTION

The object of the invention is to overcome drawbacks found with the conventional vulcanization products of epoxy group-containing acrylic elastomer, such as mentioned above, and to provide vulcanizable compositions of epoxy group-containing acrylic elastomer, which have good storage stability and long scorching time and which can afford vulcanization products with excellent compression set properties.

DETAILED DESCRIPTION OF THE INVENTION

The object of the present invention can be attained with a vulcanizable acrylic elastomer composition, which comprises copolymers of at least one of (a) an alkyl acrylate having an alkyl group having 1 to 8 carbon atoms and (b) an alkoxyalkyl acrylate having an alkoxyalkyl group having 2 to 8 carbon atoms, (c) an epoxy group-containing vinyl monomer and (d) α,β-unsaturated carboxylic acid aryl ester, and (1) a diphenyl phthalate and (2) a quaternary ammonium salt or a phosphonium salt, and (3) at least one of a urea and a guanidine as cross-linking agents.

Alkyl acrylates as component (a) for forming the acrylic elastomer include such alkyl acrylates having an alkyl group of 1 to 8 carbon atoms (including alkyl groups containing a substituent group such as a cyano group, etc.) as methyl acrylate, ethyl acrylate, n- or iso-propyl acrylate, n- or iso-butyl acrylate, n-amyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, 2-cyanoethyl acrylate, etc., and it is preferable to use ethyl acrylate or n-butyl acrylate.

Alkoxyalkyl acrylates as component (b) include such alkoxyalkyl acrylates having an alkoxyalkyl group of 2 to 8 carbon atoms as methoxymethyl acrylate, ethoxymethyl acrylate, 2-methoxyethyl acrylate, 2-ethoxyethyl acrylate, 2-butoxyethyl acrylate, etc., and it is preferable to use 2-methoxyethyl acrylate or 2-ethoxyethyl acrylate.

Both components (a) and (b) are used together usually in a ratio of component (a) to component (b) of about 10-about 90% to about 90-about 10% by mole.

A portion, that is, up to about 20% by weight, of at least one of components (a) and (b) can be substituted with other copolymerizable monomer. Such copolymerizable monomer includes, for example, ethylene, propylene, vinyl chloride, vinylidene chloride, acrylonitrile, styrene, vinyl acetate, ethyl vinyl ether, butyl vinyl ether, alkyl methacrylate, hydroxyalkyl acrylate, alkoxyalkyl methacrylate, cyclohexyl acrylate, benzyl acrylate, furfuryl acrylate, etc.

Furthermore, a portion, that is, up to about 10% by weight, of at least one of components (a) and (b) can be substituted and copolymerized with a dienic monomer. Such dienic monomer includes, for example, divinylbenzene, piperylene, isoprene, pentadiene, vinyl cyclohexene, chloroprene, butadiene, methyl butadiene, cyclopentadiene, methyl pentadiene, ethyleneglycol diacrylate, propyleneglycol diacrylate, ethyleneglycol dimethacrylate, propyleneglycol dimethacrylate, etc.

Epoxy group-containing vinyl monomer as component (c) includes, for example, vinyl glycidyl ether, allyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, etc.

Aryl ester of α,β-unsaturated carboxylic acid as component (d) includes phenyl esters, chlorophenyl esters, bromophenyl esters, nitrophenyl esters, alkylphenyl esters, alkoxyphenyl esters, etc. of such α,β-unsaturated carboxylic acids as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, etc., for example, phenyl acrylate, phenyl methacrylate, p-chlorophenyl acrylate, p-chlorophenyl methacrylate, p-bromophenyl acrylate, p-bromophenyl methacrylate, p-nitrophenyl acrylate, p-nitrophenyl methacrylate, phenyl crotonate, diphenyl maleate, diphenyl fumarate, etc.

The foregoing components are used in the copolymerization reaction in the following proportions: about 80 to 99.8% by weight preferably about 90 to 99% by weight, of at least one of component (a) and component (b), about 0.1 to about 10% by weight, preferably about 0.5 to about 5% by weight of component (c), and about 0.1 to about 10% by weight, preferably about 0.2 to about 5% by weight, of component (d).

The copolymerization reaction is carried out in the presence of an ordinary radical polymerization initiator by any one of polymerization processes such as emulsion polymerization, suspension polymerization, solution polymerization, bulk polymerization, etc., preferably by emulsion polymerization. The polymerization initiator can be used also as a redox system.

The reaction is carried out at a temperature of about -10° to about 100° C., preferably about 2° to about 80° C. in a batch-wise, continuous or intermittent fead system. After the completion of reaction, the formed polymers are recovered by separation, depending upon the type of polymerization method employed, for example, by adding a coagulating agent such as acid or polyvalent metal salts, etc. to the reaction mixture in case of emulsion polymerization or suspension polymerization and the recovered polymers are then washed and dried, and then subjected to cross-linking with a cross-linking agent.

The thus obtained, epoxy group-containing acrylic elastomer can be vulcanized with (1) a diphenyl phthalate (2) a quaternary ammonium salt or phosphonium salt, and (3) at least one of a urea and a guanidine as cross-linking agents.

The following compounds are used as these three kinds of cross-linking agents.

(1) The diphenyl phthalate for use in the present invention includes diphenyl esters of terephthalic acid, isophthalic acid and phthalic acid, preferably diphenyl esters of terephthalic acid. The phenyl ester group may optionally be substituted by a halogen, nitro group, cyano group, alkyl group or alkoxy group, and as substituted phenyl ester groups there can be mentioned for example p-nitrophenyl ester, p-chlorophenyl ester and dinitrophenyl ester.

(2) The quaternary ammonium salt and phosphonium salt for use in the present invention include compounds represented by the following formulae, respectively:

    (R.sub.1 R.sub.2 R.sub.3 R.sub.4 N).sup.+ X.sup.-

    (R.sub.1 R.sub.2 R.sub.3 R.sub.4 P).sup.+ X.sup.-

wherein

R₁ to R₄ : alkyl groups having 1 to 25 carbon atoms, alkoxy groups, aryl groups, alkylaryl groups, aralkyl groups and polyoxyalkylene groups, and two or three of these groups can be combined with N or P to form a heterocyclic structure

X⁻ : anions such as Cl⁻, Br⁻, I⁻, HSO₄ ⁻, H₂ PO₄ ⁻, RCOO⁻, ROSO₂ ⁻, RSO⁻, ROPO₂ H⁻, CO₃ ⁻⁻, etc.

The quaternary ammonium salts and phosphonium salts include, for example, such quaternary ammonium salts as tetraethylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium iodide, n-dodecyltrimethylammonium bromide, cetyldimethylbenzylammonium chloride, methylcetyldibenzylammonium bromide, cetyldimethylethylammonium bromide, octadecyltrimethylammonium bromide, cetylpyridium chloride, cetylpyridium bromide, cetylpyridium iodide, cetylpyridium sulfate, tetraethylammonium acetate, trimethylbenzylammonium benzoate, trimethylbenzylammonium-p-toluene sulfonate, trimethylbenzylammonium borate, 8-benzyl-1,8-diazabicyclo[5,4,0]undec-7-enium chloride, 1,8-diazabicyclo[5,4,0]undecene-7-methylammonium methosulfate, 5-benzyl-1,5-diazabicyclo-[4,3,0]-5-nonenium chloride, 5-benzyl-1,5-diazabicyclo[4,3,0]-5-nonenium bromide, 5-benzyl-1,5-diazabicyclo[4,3,0]-5-nonenium tetrafluoroborate, 5-benzyl-1,5-diazabicyclo[4,3,0]-5-nonenium hexafluorophosphate, etc., and such quaternary phosphonium salts as tetraphenylphosphonium chloride, triphenylbenzylphosphonium chloride, triphenylbenzylphosphonium bromide, triphenylmethoxymethylphosphonium chloride, triphenylmethylcarbonylmethylphosphonium chloride, triphenylethoxycarbonylmethylphosphonium chloride, trioctylbenzylphosphonium chloride, trioctylmethylphosphonium bromide, trioctylethylphosphonium acetate, trioctylethylphosphonium dimethylphosphate, tetraoctylphosphonium chloride, cetyldimethylbenzylphosphonium chloride, etc.

(3) The urea for use in the present invention includes urea, thiourea, thier substituted compounds such as N-methyl, N-ethyl, N,N-dimethyl, N,N'-diethyl, N,N-diethyl, N,N'-ethylidene, N-acetyl, N-methyl-N'-acetyl, N,N'-dimethylol, tetramethyl, carbamyl, N-phenyl, N-benzyl, N-ethyl-N'-phenyl, N,N'-diphenyl, N,N-diphenyl, N-benzoyl, tetraphenyl and N,N-dimethyl-N,N'-dichlorophenyl-substituted ureas, carbamoylcarbamidic acid, ethyleneurea, glycolylurea, dimethylparabanic acid, benzoimidazolone, 5-methyluracil, etc.

The guanidine for use in the present invention includes guanidine and its substituted compounds such as amino, 1,1,3,3-tetramethyl, n-dodecyl, methylol, dimethylol, 1-phenyl, 1,3-diphenyl, 1,3-di-o-tolyl, triphenyl, 1-benzyl-2,3-dimethyl and cyano-substituted guanidines, 1,6-guanidinohexane, guanylurea, biguanide, 1-o-tolylbiguanide, etc.

These cross-linking agents are used in the following proportions per 100 parts by weight of acrylic elastomer: about 0.1 to about 10 parts by weight, preferably about 0.5 to about 5 parts by weight of diphenyl phthalate; about 0.1 to about 5 parts by weight, preferably about 0.3 to about 2 parts by weight of quaternary ammonium salt or phosphonium salt; and about 0.1 to about 5 parts by weight, preferably about 0.2 to about 2 parts by weight of urea or guanidine.

These proportions are selected as preferable ranges in view of the vulcanization speed, storage stability, processing safety, properties and characteristics of the vulcanization products such as mechanical properties, heat resistance, compression set, etc. When each of these vulcanization system components is used below the lower limits of these selected proportions, the vulcanization speed is considerably lowered and the vulcanization products have no satisfactory physical properties. On the other hand, when these vulcanization system components are used above the upper limit of the selected proportions, such properties as storage stability, processing safety and physical properties of vulcanization products are deteriorated, though the vulcanization speed is increased in general.

A vulcanizable composition can be prepared by mixing these vulcanization system components together with other additives such as a reinforcing agent, a filler, an antioxidant, a stabilizer, a plasticizer, a lubricant, etc. by an ordinary mixing procedure such as roll mixing, Bambary mixing, solution mixing, etc. The vulcanization temperature of the thus prepared vulcanizable composition is usually 150° C. or higher, and vulcanization is carried out at that temperature by press vulcanization, secondary vulcanization or steam vulcanization.

The acrylic elastomer compositions of the invention are obtained by using as the epoxy group-containing acrylic elastomer, a copolymer of α,β-unsaturated carboxylic acid aryl ester, and as the crosslinking agent, a combination of specific three compounds. The so obtained compositions have good storage stability and long scorching time and can also produce vulcanization products with excellent compression set properties.

The present invention will be explained in detail below, referring to the Examples.

EXAMPLES 1 TO 6 AND COMPARATIVE EXAMPLES 1 TO 4

One hundred and fifty parts by weight of water, 0.1 part by weight of sodium sulfate, 5.5 parts by weight of a mixture of Emerl 10, Emulgen 147 and Levenol WZ (products made by Kao K. K., Japan) in a ratio of 1.5:2:2 as an emulsifier and 100 parts by weight of monomer mixture shown in Table 1 were charged into a separable flask provided with a thermometer, a stirrer, a nitrogen gas inlet and an evacuating means, and oxygen was thoroughly removed from the flask by repetitions of evacuation and nitrogen replacement EMAL 10 is Sodium lauryl sulfate, Emulgen 147 is polyoxyethylene lauryl ether and Levenol WZ is sodium polyoxyethylene alkylphenyl ether sulfate. Then, a mixture of the following polymerization initiators

Sodium hydrosulfite: 0.01 part by weight

Sodium formaldehyde sulfoxylate: 0.002 parts by weight.

Tertiarybutyl hydroperoxide 0.005 parts by weight was added thereto and the polymerization mixture was subjected to polymerization at room temperature for 6 hours so that the polymerization conversion was within the range of 95 to 99%. Then, the polymerization reaction mixture was salted out, thoroughly washed with water and dried, whereby a copolymer elastomers A˜G were obtained.

                  TABLE 1                                                          ______________________________________                                         Monomer      Acrylic elastomer                                                 (parts by weight)                                                                           A      B      C    D    E    F    G                               ______________________________________                                         Ethyl acrylate                                                                              50     50     96.8 60   50   50   50                              n-Butyl acrylate                                                                            30     30          36.8 50   30   30                              2-Methoxyethyl                                                                              16.8   16.8             16.7 18.5 18                              acrylate                                                                       Allyl glycidyl ether                                                                               2                           2                              Glycidyl methacrylate                                                                       1.5           1.5  1.5  1.5  1.5                                  Phenyl methacrylate                                                                         1.7    1.7    1.7  1.7                                            p-Cyanophenyl                        1.8                                       acrylate                                                                       ______________________________________                                    

Vulcanizable compositions were prepared from the acrylic elastomers obtained in Examples and Comparative Examples by open rolls with cooling according to the mixing formula shown in Table 2, and subjected to press vulcanization at 180° C. for 10 minutes and secondary vulcanization in a gear oven at 175° C. for 4 hours. The thus obtained press vulcanization products and secondary vulcanization products were subjected to determination of vulcanization physical properties according to JIS K-6301. The results are shown also in Table 2 together with the scorch time (125° C., Ts). The compression set was determined at 25% compression at 150° C. for 70 or 500 hours.

                                      TABLE 2                                      __________________________________________________________________________                                                    Comp.                                                                              Comp.                                                                              Comp.                                                                              Comp.               Examples and Comparative Examples                                                                     Ex. 1                                                                              Ex. 2                                                                              Ex. 3                                                                              Ex. 4                                                                              Ex. 5                                                                              Ex. 6                                                                              Ex. 1                                                                              Ex. 2                                                                              Ex.                                                                                Ex.                 __________________________________________________________________________                                                                4                               Acrylic elastomer                                                                         A   A   B   C   D   E   A   F   G   G                               used                                                               Formula     Stearic acid                                                                              1   1   1   1   1   1   1   1   1   1                   (parts by weight)                                                                          FEF carbon black                                                                          70  70  70  70  70  70  70  70  70  70                              Antioxidant (Noguard                                                                      2   2   2   2   2   2   2   2   2   2                               445, made by                                                                   Uniroyal)                                                                      Bis(p-nitrophenyl)tere-                                                                   2.1 1.7 2.1 2.1 2.1 2.1     2.1 2.1                                 phthalate                                                                      Tetrabutylammonium                                                                        0.5     0.5 0.5 0.5 0.5 0.5 0.5 0.5                                 bromide                                                                        Octadecyltrimethyl-                                                                           1                                                               ammonium bromide                                                               Diphenylurea                                                                              0.4     0.4 0.4 0.4 0.4                                             Ammonium benzoate                              2                               Scorch time (min.)                                                                        26.9                                                                               15.3                                                                               37.3                                                                               22.1                                                                               28.0                                                                               9.2 53.2                                                                               12.1                                                                               20.4                                                                               20.4                Press vulcanization                                                                        Hardness (JIS-A)                                                                          71  70  68  70  70  72  62  68  68  66                  products    100% Modulus                                                                              58  53  47  61  56  63  36  46  41  48                              (kg/cm.sup.2)                                                                  Tensile strength                                                                          107 102 98  123 111 120 88  93  90  113                             (kg/cm.sup.2)                                                                  Elongation (%)                                                                            236 257 295 219 233 206 382 255 263 268                             Compression set                                                                           31  28  38  36  36  24  53  41  47  55                              (70 hrs) (%)                                                       Secondary vulcanization                                                                    Hardness (JIS-A)                                                                          79  74  72  78  78  81  66  70  70  71                  products    100% Modulus                                                                              98  68  66  92  84  110 44  58  54  70                              (kg/cm.sup.2)                                                                  Tensile strength                                                                          123 120 109 138 128 132 96  115 102 125                             (kg/cm.sup.2)                                                                  Elongation (%)                                                                            150 208 230 152 179 148 287 201 241 200                             Compression set                                                                           9   13  18  10  12  8   29  18  21  32                              (70 hrs) (%)                                                                   Compression set                                                                           28  33  42  27  30  21  48  44  50  51                              (500 hrs) (%)                                                      __________________________________________________________________________ 

What is claimed is:
 1. A vulcanizable acrylic elastomer composition having improved compression set properties which comprises copolymers of(a) an alkyl acrylate having an alkyl group having 1 to 8 carbon atoms, and (b) an alkoxyalkyl acrylate having an alkoxyalkyl group having 2 to 8 carbon atoms, and (c) an epoxy group-containing vinyl monomer, and (d) alpha, beta-unsaturated carboxylic acid aryl ester,and a combination of cross-linking agents that includes: (1) a diphenyl phthalate, and (1) a quaternary ammonium salt or a phosphonium salt, and (3) at least one of a urea compound and a guanidine compound.
 2. A composition according to claim 1 wherein the weight percentages of the listed components based on the total weight of the copolymer are as follows:(a) +(b) 80-99.8 (c) 0.1-10 (d) 0.1-10.
 3. A composition according to claim 1 wherein the parts by weight of the cross-linking agents based on 100 parts by weight of the acrylic elastomer are(1) 0.1-10 (2) 0.1-5 (3) 0.2-2.
 4. A composition according to claim 2 wherein the parts by weight of the cross-linking agents based on 100 parts by weight of the acrylic elastomer are(1) 0.1-10 (2) 0.1-5 (3) 0.2-2.
 5. A vulcanizable acrylic elastomer composition having improved compression set properties which comprises copolymers of at least one of (a) and (b)(a) an alkyl acrylate having an alkyl group having 1 to 8 carbon atoms, and (b) an alkoxyalkyl acrylate having an alkoxyalkyl group having 2 to 8 carbon atoms, and (c) an epoxy group-containing vinyl monomer, and (d) alpha, beta-unsaturated carboxylic acid aryl ester,and a combination of cross-linking agents that includes: (1) a diphenyl phthalate, and (2) a quaternary ammonium salt or a phosphonium salt, and (3) at least one of a urea compound and a guanidine compound.
 6. A composition according to claim 5 wherein the weight percentages of the listed components based on the total weight of the copolymer are as follows:(a) or (b) 80-99.8 (c) 0.1-10 (d) 0.1-10.
 7. A composition according to claim 5 wherein the parts by weight of the cross-linking agents based on 100 parts by weight of the acrylic elastomer are(1) 0.1-10 (2) 0.1-5 (3) 0.2-2.
 8. A composition according to claim 6 wherein the parts by weight of the cross-linking agents based on 100 parts by weight of the acrylic elastomer are(1) 0.1-10 (2) 0.1-5 (3) 0.2-2. 